Four fish rhabdoviruses have been identified as the etiological agents of economically important diseases in fish (carp, pike, trout and salmon) as evidenced by losses incurred in both European or American fish hatcheries. Initial studies have indicated that structurally these viruses differ both from each other and from the well-studied rhabdovirus vesicular stomatitis virus. The nature of these differences and their effect upon the respective virus infections and replication processes will be studied. Both molecular and genetic approaches will be undertaken in order to gain an insight into how these viruses replicate in permissive cells. A second major directive of this proposal will be to establish, in model tissue culture systems, persistent infections of spring viremia of carp virus (SVCV) in order to elucidate the nature of such infections. Asymptomatic carrier states of carp have been implicated to be involved in disease transmission, although the nature of such carrier states has not been identified. A second aim of this second directive will therefore be to characterize the nature of virus infection in tissue (obtained from Dr. Barry Hill of the Ministry of Agriculture and Fisheries) derived from asymptomatic carrier fish. In addition we will supply Dr. Hill with mutant, attentuated and/or host-restricted SVCV for use in carp infections and protection from virulent challenge.